Sample containers, often called sample bottles or samplers, for collection of samples of petroleum fluids as well as other fluids, are well known in the art. A typical objective is to sample representative samples of a process fluid at a specific processing stage. In order to achieve the objective, it is crucial that the fluid pressure is maintained during the sampling procedure. Other parameters known in the art are constant temperature and no mixing with non-representative fluid, such as fluid left in dead volumes in the sample bottle or its connections.
A typical sample bottle design is to have a divided chamber with a movable piston between the chambers. One part of the chamber contains a pressurized back pressure fluid, for which the pressure typically equals the pressure of the process fluid to be sampled. The other part of the divided chamber is the sample chamber, into which the sample is brought without fluctuating the pressure too much. Thereby pressure induced phase transformations of the fluid phases are reduced or avoided.
Another type of sample containers has a single sample volume, and such sample containers are typically connected as a parallel flow of a process stream. Flowing a fraction of the process flow through the sample container for a while, provides, at least in theory, a representative sample that can be isolated from the stream without fluctuating the pressure too much.
However, free gas flotation during container filling and dissolved gas flotation during container filling or pressure release often cause severe problems, particularly for (oil in) water and (water in) oil sample collection and analysis. Said flotation problems are caused by inappropriate sample bottle designs and methods of operation or both, which will be further explained below. The flotation problem is relevant for being able to sample more realistic samples in order to optimize process and equipment operation, such as the separation process of cleaning produced water down to very low oil contents (currently 30 ppm) allowable for discharge to sea. Other typical problems are related to the length or morphology of the inlet tubing which often affect the fluid qualities by causing shear forces and pressure drop to the flowing fluids. Currently, portable sampling solutions often have a limited ability of collecting samples at high gas/liquid fractions. Furthermore, liquid volumes are typically small for portable sample devices, which sometimes is a disadvantage for subsequent sample analysis since dynamic fluctuations and intermediate process abnormalities have larger effect for small volumes.
Transport regulations may pose a limitation on transport of sample bottles. A typical procedure is depressurization to below bubble point before transport to a laboratory, after which the sample is recombined/recovered in the laboratory for analysis.
Two relevant prior art sample containers are described and illustrated in the patent publications U.S. Pat. No. 7,024,951 and U.S. Pat. No. 6,182,505, however the sample container of U.S. Pat. No. 7,024,851 has a flotation problem and the teaching of U.S. Pat. No. 6,182,505 merely relates to finding volume fractions of phases. Some description of the underlying problem of the present invention can be found in patent publication U.S. Pat. No. 4,844,817, from column 6, and in the paper “Diagnosing and Resolving Chemical and Mechanical Problems with Produced Water Treating Systems” by Frankiewicz, et al. 12th Annual International Petroleum Environmental Conference (IPEC); November 2005.
A demand exists for improved sample containers and methods for sample collection, particularly for collecting oil-in-water and water-in-oil samples not affected significantly by gas flotation effects. The objective of the invention is to meet the demand.